JP2015107903A - Tin sulfide sintered body and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tin sulfide sintered body having uniform specific resistance by reducing the specific resistance.SOLUTION: The tin sulfide sintered body preferably contains each of Bi, Fe, Sb, As, P of 100 ppm or less by mass ratio and has a specific resistance of 0.001 Ω cm to 10 Ω cm, and 0≤x≤0.01 and y/z ratio in a range of 0.90 to 1.01 in a composition formula (SnS)(CuS). It preferably contains Cu or Ag at 100 ppm or more and less than 10000 ppm. The tin sulfide sintered body can be suitably used as a sputtering target during manufacturing CZTS series thin film solar cells.

Description

  The present invention relates to a tin sulfide sintered body suitable for a sputtering target for forming a buffer film or an optical film of a solar cell by a direct current (DC) sputtering method and a method for producing the same.

  In recent years, as a thin film solar cell using a compound semiconductor for a light absorption layer, it is called a CZTS thin film solar cell. Copper (Cu), zinc (Zn), tin (Sn), and sulfur (S ) Or selenium (Se), a thin film solar cell using a compound semiconductor composed of a chalcogen element has attracted attention (see Non-Patent Document 1 and Non-Patent Document 2).

  Unlike the CIS and CIGS thin film solar cells, this CZTS thin film solar cell is expected to be used in the future because it does not use rare elements such as indium (In). Further, since a conversion efficiency can be expected even with sulfides not using Se, it is also expected as a solar cell that does not contain highly toxic Se.

Cu ₂ ZnSnS ₄ is also attracting attention as a photocatalyst that decomposes water with sunlight to generate hydrogen (see Non-Patent Document 3).

  However, at present, high conversion efficiency like CIS and CIGS thin film solar cells has not been obtained, and further research and development is required.

  As a general method for producing a CZTS film, various methods such as a physical vapor deposition method such as a sputtering method and vapor deposition, a sol-gel method, a spray pyrolysis method, and an electrodeposition / sulfurization method have been proposed (see Non-Patent Document 2). ).

For example, in Patent Document 1, as a method for producing a CZTS-based light absorption layer constituting a conventional CZTS-based thin film solar cell, a precursor film that is a stacked film of Cu, Zn, and Sn is formed on an electrode layer by a sputtering method or the like. A method of heat-treating this in a hydrogen sulfide (H ₂ S) atmosphere is disclosed.

In addition, development of synthesizing a compound layer of CuZnSnS ₃ using a sulfide target such as ZnS, Cu ₂ S, or SnS ₂ is in progress (see Non-Patent Document 4 and Patent Document 5).

  In the method of sulfiding using a metal target, since the vapor pressure of Zn is high, there is a possibility that Zn volatilizes and Zn is reduced, or a large volume change occurs during sulfidation, and the film may be peeled off from the substrate.

  In Patent Document 6, CuS (copper sulfide) powder, ZnS powder and tin sulfide powder are mixed, a single phase target of CZTS is prepared by hot pressing, and the surface resistance is 45.3Ω with a p-type conductor. There is a description that a sintered body of / □ to 680Ω / □ was obtained.

  Moreover, it is pointed out that the conversion efficiency of the solar cell is increased with a composition with a large amount of Zn and a small amount of Cu (see Non-Patent Document 5). Therefore, a film forming method that can control the composition ratio using a target of tin sulfide, zinc sulfide, or copper sulfide instead of a compound target having a stoichiometric composition of CZTS has been studied.

  As shown in FIG. 5, the sputtering method is a film forming method in which a target is irradiated with Ar ions and a substance released from the target is stacked on a substrate facing the target. Ar ions are irradiated onto the target by setting the target surface to a negative potential, and electrons and targets are emitted from the target by ion irradiation. Ar ion irradiation (discharge) is sustained by supplying irradiation ions and charges of emitted electrons from the electrodes.

  The sputtering method includes a method using a direct current (DC) power source and a method using a high frequency (RF) as a charge supply method. Generally, a DC power source is used when the resistance of the target material is low, and an RF power source is used when the resistance is high. The RF sputtering method can sputter even on a target with high resistance. However, the power source is higher than the DC power source, and it is necessary to adjust the matching between the electric resistance and the electric capacity in the high frequency circuit in order to make the target surface have a negative potential. Cost more than.

  Since sulfide targets such as SnS targets have high resistance and cannot perform direct current discharge, it is difficult to form a film by a DC sputtering method, and it is required to reduce the resistance of a tin sulfide target.

  A low resistance tin sulfide target can be obtained by lowering the resistance of the tin sulfide particles themselves. The tin sulfide particles are sintered and mixed with conductive particles and sintered. There is a way to get it.

In a ZnS-SiO ₂ mixed target used for a protective film for an optical disk, ZnS, SiO ₂ and In ₂ O ₃ , zinc oxide, tin oxide, antimony oxide and other conductive oxides are mixed, and hot pressing or hot isostatic pressure is performed. A target has been proposed in which the resistance of the target is lowered by sintering by a pressing method and DC sputtering is possible (see Patent Documents 2 and 3). Also proposed is a method of reducing the resistance by adding Al, Ag, Cu, In ₂ S ₃ and ZnCl ₂ powders to ZnS, baking, and adding Al, Ag, Cu, In, Cl to ZnS. (See Patent Document 4).

  In the method of mixing and sintering with conductive particles, as shown in FIG. 2 (a), the conductive particles are connected to form a low-resistance conductive path, whereby charges flow through the conductive path and the target. The surface potential becomes negative. However, when the number of conductive particles is small or when they cannot be mixed uniformly, the conductive particles are not connected and a conductive path is not formed as shown in FIG. As described above, when the conductive oxide is included, there is a problem that the resistance of the target is not lowered unless the conductive path is formed by connecting the conductive particles.

When mixing metal powders, metal particles such as Al, Ag, Cu, and In are soft, so it is difficult to uniformly mix sulfide powders, and there is a problem that compositional variation and resistance distribution of the obtained target are large. is there. Further, since Al is active, there is a problem that if it is made into a fine powder, it tends to ignite and is difficult to handle. Even if Cu, In, Al, or Ga is added as a metal, these metals are more easily sulfided than SnS. Therefore, during sintering, sulfurization of Cu ₂ S, In ₂ S ₃ , Al ₂ S _3, and Ga ₂ S ₃ is performed. Forming a metal Sn. Since the metal Sn has a low melting point, it oozes out from the sintered body during sintering and precipitates between the molds to fix the mold, or segregates at the lower part of the sintered body.

  By the way, it is known that tin sulfide is a semiconductor, and by replacing the atomic position of tin with another element, for example, monovalent Ag, it becomes a p-type semiconductor, and when it is substituted with pentavalent Sb, it becomes an n-type semiconductor. (See Non-Patent Document 6). Therefore, adding monovalent or pentavalent metal elements to tin sulfide reduces the resistance, but adding monovalent and pentavalent elements simultaneously traps free electrons in acceptors and holes in donor electrons (compensation). Therefore, the resistance is difficult to decrease. Therefore, it is necessary to add monovalent or pentavalent elements in excess of other elements, or to high-purity tin sulfide (SnS) free from other elements. If the tin sulfide powder thus produced is sintered, a low resistance sintered body can be obtained.

Further, in the compound semiconductor, the defect of the constituent element (self-defect) forms an electron level in the band. Tin sulfide (SnS) has Sn vacancies and S vacancies, and the concentration is calculated to be 10 ¹⁴ cm ⁻³ to 10 ¹⁸ cm ⁻³ or less (see Non-Patent Document 7). These defects do not affect the electrical characteristics when the amount of electrically active impurities is more than several tens of ppm, but are affected by high-purity tin sulfide (SnS). In high-purity tin sulfide (SnS), if an additive element higher than these self-defect concentrations is added, the conductivity must be controlled.

  Thus, although the general principle of making tin sulfide (SnS) have a low resistance has been known, an effective low resistance SnS powder is difficult to obtain, and a commercially available tin sulfide powder is also available. There is no known method for reducing the resistance. Furthermore, a specific method for easily reducing the resistance of a tin sulfide (SnS) sintered body and having a uniform specific resistance has not been known. Further, since tin sulfide (SnS) is easily sputtered, when a metal such as Cu is deposited in the target, the lower part of the portion where Cu is deposited at a low sputtering rate remains unexcavated. As a result, as shown in FIG. There are also problems such as the formation of a convex portion and the occurrence of abnormal discharge.

JP 2009-026891 A JP 2001-192820 A JP 2007-310994 A Japanese Patent Laid-Open No. 2002-373459 Special table 2012-507631 gazette JP 2010-245238 A

K. ITO T. NAKAZAWA JJAP 27 (1988) 2094 Hironori Katagiri Electronic Materials November 2009 45 D. YOKOYAMA et al. Appl. Phys Express 3 (2010) 101202 Shigeo Igarashi, Takuro Seki, Narushiro Momose, Yoshio Hashimoto, Kentaro Ito: Proceedings of the 57th Joint Conference on Applied Physics 20p-TE-7 (2010) 14-254 H. Katagiri et al. Thin Solid Films 517 (2009) 2455 W. Alberts, C.I. Hass, H.H. J. et al. Vink and J.M. D. Wascher J. et al. Appl. Phys. 32 (1961) 2220 J. et al. Vial et. al. Appl. Phys. Lett. , 100 (2012) 032104 J. et al. Vial et. al. Appl. Phys. Lett. , 100 (2012) 032104 Kazuo Koike Resources and Materials 109 (1993) 23-28

  The object to be solved by the present invention is a tin sulfide sintered body that can be used as a sputtering target during the production of a CZTS-based thin film solar cell. The specific resistance of the tin sulfide sintered body is made stable so that direct current sputtering is possible. An object of the present invention is to provide a tin sulfide sintered body that has a reduced specific resistance.

As a result of intensive studies in order to solve the various technical problems, the present inventor has found that each of the impurity elements contained in the tin sulfide sintered body contains 100 ppm or less of Bi, Fe, Sb, As, and P. that, in the formula _{(Sn y S z) 1-} x (Cu 2 S) x, is 0 ≦ x ≦ 0.01, y / z ratio and the range of 0.90 or more 1.01 or less Furthermore, the specific resistance of the tin sulfide target can be reduced to 0.001 Ω · cm to 10 Ω · cm by containing Cu at 100 ppm or more and less than 10,000 ppm, and stable film formation is suppressed by suppressing abnormal discharge due to nodules. As a result, the present invention has been completed. Specifically, the present invention provides the following.

(1) Bi, Fe, Sb , As, P, but is at 100ppm or less at each mass ratio, in the composition formula _{(Sn y S z) 1-} x (Cu 2 S) x, in 0 ≦ x ≦ 0.01 And the y / z ratio is 0.90 or more and 1.01 or less,
A tin sulfide sintered body having a specific resistance of 0.001 Ω · cm to 10 Ω · cm.

  (2) The tin sulfide sintered body according to (1), which contains 100 ppm or more and less than 10,000 ppm of Cu or Ag.

  (3) The tin sulfide sintered body according to (1) or (2), which is used as a target for DC sputtering.

(4) In the formula _{(Sn y S z) 1-} x (Cu 2 S) x, 0 ≦ x ≦ a 0.01, DC sputtering target ratio y / z is 0.90 or more 1.01 or less A method for producing a tin sulfide sintered body for
A tin sulfide powder containing 0 to 0.01% by mass of Cu, Bi, Fe, Sb, As, P is 100 ppm or less by mass ratio, and an average particle size is 100 μm or less,
A method for producing a tin sulfide sintered body, wherein the tin sulfide powder is sintered by the following A) or B) to obtain a sintered body.
A) A normal pressure sintering method in which the temperature is maintained at 600 to 800 ° C. in an inert gas atmosphere under normal pressure.
B) A hot press method in which the material is heated and held in an inert gas atmosphere at a pressure of 15 kg weight / cm ² or more and 400 kg weight / cm ² or less at a temperature of 500 to 800 ° C.

  According to the tin sulfide sintered body of the present invention, the specific resistance can be 0.001 Ω · cm to 10 Ω · cm, and if this sintered body is used as a sputtering target, there is no occurrence of abnormal discharge or nodules and it is stable. DC sputtering is possible.

  Further, according to the method for producing a tin sulfide sintered body of the present invention, a tin sulfide sintered body having low specific resistance, stable quality, and improved safety can be produced.

  Furthermore, according to the method for producing a CZTS film of the present invention, even when a tin sulfide sintered body is used as a target, direct current sputtering can be used, so that it can be produced at low cost.

It is a figure explaining the carrier generation | occurrence | production mechanism in tin sulfide (SnS), and the mechanism of high resistance. It is a schematic diagram which shows the electroconductive path in the mixed sintered compact of electroconductive particle and a tin sulfide (SnS) particle | grain. FIG. 3 is a schematic diagram showing a simple mixed state a) before sintering and a state b) in which the eutectic liquid covers the particles by reacting on the surface of tin sulfide (SnS) particles. It is a figure which shows the structure of the target for sputtering. It is a schematic diagram which shows a general sputtering process. It is a schematic diagram which shows the charge of the SnS target by Ar ion irradiation, and the neutralization by an electron. 10 is a SEM photograph showing a sputtering surface of Comparative Example 5. This is the amount of change in sputtering voltage between Example 1 and Comparative Example 5. It is an XRD pattern of tin sulfide of Example 1 and Comparative Example 6. It is the amount of change in the free energy of the cast due to the reaction between Sn and Cu ₂ S.

The present invention is described in detail below.
<Effects of electrical properties on specific resistance due to impurities contained in tin sulfide sintered body>
In the tin sulfide sintered body of the present invention, Bi, Fe, Sb, As, and P are each 100 ppm or less, preferably 50 ppm or less. If any of Bi, Fe, Sb, As, and P exceeds 100 ppm, a low resistance of 0.001 Ω · cm to 10 Ω · cm cannot be obtained as the specific resistance of the tin sulfide sintered body as described in detail below. .

Tin sulfide is a compound having characteristics as a semiconductor. In general, the resistance ρ of a semiconductor is expressed by the following equation (1) from the charge q, carrier density n, and mobility v of a semiconductor carrier.
ρ = 1 / (qnv) (1)
Therefore, the resistance decreases as the carrier density or mobility of the semiconductor increases. In general, it is difficult to increase the mobility, but the carrier density can be controlled by adding impurities. Therefore, in semiconductors, the carrier concentration is increased to lower the resistance.

  As shown in FIG. 1, carriers in a semiconductor are holes in a p-type semiconductor and free electrons in an n-type semiconductor, and holes are impurity levels (acceptor level) created in the band by an element added to the semiconductor. It is generated when electrons in the conduction band are excited. Free electrons are generated by exciting the impurity level (donor level) electrons created in the band by the added element to the conduction band. These impurity levels are as small as several meV to several tens meV from the band edge and can be excited at room temperature.

  On the other hand, there is an impurity element that forms an electron level at 100 meV or more from the band edge. These electron levels are called deep levels because they cannot be excited at room temperature. When the concentration of these levels is Na (acceptor concentration), Ne (deep concentration), and Nd (donor concentration), respectively, a p-type semiconductor in the case of Na> Nd + Ne, and an n-type in the case of Ne> Nd + Na. It becomes a semiconductor and its resistance is low.

  However, in the case of Nd ≧ Na and Nd ≧ Ne, the acceptor level is occupied by deep level electrons, and the donor level electrons transition to the deep level, so the carrier concentration decreases and the resistance increases. . If Na or Ne is larger than Nd, carriers are generated. However, when Nd traps an electron of Ne and ionizes it, or when an electron transitions to Na and ionizes, the mobility is lowered because the carrier is scattered. Therefore, it is preferable that Nd is small.

  From the above general theory regarding the electrical characteristics of the semiconductor, the present inventors have proposed that in order to reduce the specific resistance of the tin sulfide sintered body (SnS), Bi, Fe, Sb, As, P, which form deep levels, are formed. It has been found that it is important to add an element such as Cu that reduces impurity elements such as Cu and generates carriers.

  For example, when research on deep level formation mechanisms advances with the practical application of semiconductors such as Si and GaAs, transition metal such as Fe, Co and Ni, Au and compound semiconductor vacancies and self-defects form deep levels. It is said. In SnS, the elements that form deep levels are unknown, but transition metals such as Fe, Co, and Ni are considered to form deep levels.

In compound semiconductors, defects of constituent elements, that is, Sn vacancies and S vacancies form deep levels. The concentration is said to be 10 ¹⁸ cm ⁻³ or less (about 10 ppm). Therefore, when the impurity concentration is 100 ppm or less, carriers generated from this defect become the main carriers of SnS. Here, Bi, Sb, As, and P are considered to form a donor level. Since these compensate for the acceptor level of Cu and S vacancies, the carrier concentration does not increase. Further, when there are many ionized impurities, carriers are scattered and the mobility is lowered. Therefore, when these impurities are contained, the resistance is increased.

  In general, in a CZTS solar cell, n-type CdS or ZnS is formed on a p-type or high-resistance CZTS layer to form a pn junction or a pin junction. Therefore, it is better for the raw material of CZTS to have less n-type impurities. Therefore, the element added to reduce the resistance of the tin sulfide sintered body (SnS) is preferably Cu or Ag, which is said to be p-type.

  The concentration added so that the tin sulfide sintered body becomes p-type needs to add at least 10 ppm of Cu and Ag so that Na> Nd + Ne described above, so that the effect of the present invention is surely exhibited. It is preferable to add 100 ppm or more. The solid solubility limit of Cu or Ag with respect to SnS is not clear, but generally it is preferably less than 10000 ppm, more preferably 5000 ppm or less because mobility decreases when added in large amounts.

<Method for producing high-purity tin sulfide powder>
As described above, in order to obtain the tin sulfide sintered body of the present invention, the tin sulfide powder as a raw material requires high-purity tin sulfide powder with controlled impurities.

As a method for producing high-purity tin sulfide (SnS) powder, ampules are encapsulated using high-purity Sn and high-purity S produced by electrolysis, etc., and heated to, for example, 900 ° C. above the melting point of SnS (885 ° C.). A method for producing an ingot by pulverization and a high-purity Sn atomizing method to produce high-purity Sn particles of 100 μm or less and reacting it with H ₂ S or S vapor, stannous chloride or tin sulfate There is known a wet method of adding an aqueous solution of a hydrogen sulfide gas, a sodium hydrosulfide (NaSH) solution or an aqueous solution of a sulfide selected from ammonium sulfide, ammonium polysulfide, thiourea and thioacetamide to an aqueous solution of a divalent salt such as .

  However, in the method of pulverizing the ingot, it is difficult to control the impurity concentration and the particle size by pulverization. Moreover, since the high purity raw material is not commercially available and difficult to obtain in the wet method, it is difficult to achieve high purity. On the other hand, a method of sulfiding using high-purity Sn particles and high-purity S can relatively easily obtain a high-purity SnS powder. For this reason, in the present invention, it is preferable to produce by the dry method described above.

<Cu addition method>
As a method for adding Cu to make the tin sulfide sintered body p-type, there is a method in which high-purity Sn and Cu are simultaneously melted and atomized to produce Cu-added Sn particles. It is difficult to uniformly disperse a specific amount of Cu in Sn.

In general, it is known that copper sulfide (Cu ₂ S) is easily reduced in resistance. There is a possibility that a sintered body having a low resistance can be obtained by mixing and sintering Cu ₂ S and SnS. As shown in the phase diagram of SnS—Cu ₂ S in Non-Patent Document 8, Cu ₂ S and SnS undergo a eutectic reaction and a liquid phase is generated at 490 ° C. or higher. Therefore 490 ° C. or higher in the eutectic composition in the following liquidus temperature _{(Cu 2 S: 55mol%,} SnS: 45mol%) in than SnS excess composition region coexist SnS and SnS-Cu ₂ S eutectic liquid phases.

The present invention found that swinging the amount of Cu 2 _S is added to SnS, result of studying in detail the sintering at various temperatures, in SnS sintered body obtained by adding a specific amount of Cu 2 _S, resistance is low It has been found that a sintered body can be obtained. This is because, as shown in FIG. 3, the mixed state a) in which Cu ₂ S is mixed with SnS reacts on the surface of the SnS particles during the process of heating and sintering, thereby producing a eutectic liquid phase. It is estimated that this eutectic liquid covers the particle surface, and a low-resistance layer is formed on the SnS particle surface, which is connected by sintering to form a state b) in which conductive paths are connected and resistance is reduced. The Further, since Cu diffuses from the liquid phase into the SnS particles, it is presumed that the surface of the SnS particles is a p-type low resistance layer.

Furthermore, from the thermodynamic consideration of the formation energy of SnS and Cu ₂ S, if metal Sn is present at a temperature lower than 450 ° C. as shown in FIG. 10, the cast free energy change of the following chemical reaction becomes negative, and the reaction Advances to the right and metal Cu is deposited. Therefore, the eutectic reaction of SnS—Cu ₂ S does not occur.
Cu ₂ S + Sn = SnS + 2Cu

Thus, in the formula _{(Sn y S z) 1-} x (Cu 2 S) x, the composition ratio of Cu ₂ S is 0 ≦ x ≦ 0.01, y / z ratio is Sn / S ratio of SnS Is important to be within the range of 0.90 to 1.01. In the composition range where the Sn / S ratio (y / z ratio) exceeds 1.01, Cu precipitates in the sintered body and causes abnormal discharge. In addition, when the composition range is less than 0.90, that is, when S is large and excessive, polysulfide phases such as SnS ₂ and Sn ₂ S ₃ are mixed and the sintered density does not increase.

<Method for producing tin sulfide sintered body>
The high-purity tin sulfide (SnS) powder produced by the above method is weighed as the raw material powder. Alternatively, a predetermined amount of high-purity tin sulfide (SnS) powder and high-purity copper sulfide (Cu ₂ S) powder prepared by the above method are weighed and mixed. Mixing can be performed by a known method such as a mortar, V blender or wet ball mill.

  Next, the mixture of the raw material powders obtained above is sintered. As a sintering method, A) normal pressure sintering method or B) hot press (HP) method can be used.

  A) In the atmospheric pressure sintering method, first, the obtained mixed powder is put into a mold and press-molded. Or it shape | molds with a cold isostatic press (CIP), and produces a molded object. The molded body is sintered by heating and holding at 600 ° C. or higher, more preferably 640 ° C. or higher, and the upper limit is 800 ° C. or lower, more preferably 750 ° C. or lower. If the temperature is lower than 600 ° C., it is difficult to sinter and the relative density becomes low, which is not preferable, and if it exceeds 800 ° C., the dissociation of sulfur occurs vigorously. Sintering is preferably performed in an inert gas atmosphere such as Ar or nitrogen gas because SnS is a sulfide and sulfur dissociates at a high temperature.

  B) In the hot press (HP) method, which is a pressure sintering method, the obtained mixed powder is packed in a graphite mold, placed in a hot press apparatus, and sintered under pressure. The sintering temperature is 500 ° C. or higher, more preferably 600 ° C. or higher, and the upper limit is 800 ° C. or lower, more preferably 730 ° C. or lower. If it is 500 ° C. or lower, sintering is difficult and the relative density is low, which is not preferable. If it exceeds 800 ° C., the melt in the sintered body increases and the melt is pushed out of the mold.

When copper sulfide (Cu ₂ S) is not mixed, the higher the pressure applied, the higher the density. The pressurizing pressure is 15 kg weight / cm ² or more, more preferably 50 kg weight / cm ² or more, and the upper limit is 400 kg weight / cm ² or less, preferably 300 kg weight / cm ² or less. If it is less than 15 kg weight / cm ² , sintering does not proceed. ^{On the other hand} , if it exceeds 400 kg weight / cm ² , the liquid phase is pushed out and a low resistance layer is not formed on the tin sulfide (SnS) particles, which is not preferable.

When mixing copper sulfide (Cu ₂ S), 15 kgf / cm ² or more, more preferably 50 kgf / cm ² or more, 200 kgf / cm ² or less, more preferably 175 kgf / cm ² or less is good. If it is less than 15 kg weight / cm ² , sintering does not proceed. ^{On the other hand} , if it exceeds 175 kgf / cm ² , the liquid phase is pushed out and a low resistance layer is not formed on the tin sulfide (SnS) particles, which is not preferable.

The pressurization pattern is that after the raw materials are packed in the mold, pressurization is performed to compress the mixed powder of the mold, and then the pressure is released and heated to about 500 ° C. to stir tin sulfide (SnS) and copper sulfide (Cu ₂ S). Sintering may be advanced by pressurizing after the liquid phase is produced by the reaction. A release material may be applied to the graphite mold in order to prevent the sintered body from sticking. The release material such as BN, _Al 2 _{O 3,} or _the may be used.

  Sintering is preferably performed in an inert gas atmosphere such as Ar or nitrogen gas because SnS is a sulfide and sulfur dissociates at a high temperature. Further, it may be heated in a vacuum from room temperature to about 550 ° C. to remove adsorbed substances such as moisture, and then filled with an inert gas.

A eutectic composition for uniformly adding Cu can be prepared by the following procedure. A predetermined amount of tin sulfide (SnS) and copper sulfide (Cu ₂ S) are mixed, heated and melted, and pulverized. SnS and Cu ₂ S show a eutectic reaction throughout the region as shown in Non-Patent Document 8. The ratio of tin sulfide (SnS) and copper sulfide (Cu ₂ S) is preferably SnS 49 mol% or more and 75 mol% or less, which melts at an SnS excess composition, 700 ° C. or less. Except Cu, which is solid-solved in SnS, it is precipitated as a eutectic structure of Cu ₂ S and SnS. When producing by the hot press method, most of the liquid phase of Cu ₂ S and SnS is extruded, and Cu which is balanced at the sintering temperature is dissolved in the sintered body.

  Hereinafter, the present invention will be described using examples.

<Example 1>
(Preparation of high-purity tin sulfide (SnS) particles)
First, Sn powder having a particle size of 38 μm or less and a purity of 3N (manufactured by Kojundo Chemical Laboratory, SNE04PB) and sulfur powder of 4N purity (manufactured by Kosei Chemical Laboratory, SSE02PB) are used in a molar ratio of 1: 2. Were mixed in a mortar and placed in an alumina crucible. Alumina crucible containing raw material powder is put in a graphite container, covered, heated to 200 ° C. in a vacuum using an electric furnace, then heated to 550 ° C. in a nitrogen atmosphere, held for 1 hour, The heating was stopped and the system was cooled.

  The XRD pattern of the produced sulfide is shown in FIG. The XRD measurement results of the tin sulfide (SnS) particles of the present invention and the XRD patterns of the γ-Sn (generated at 161 ° C. or higher) phase and the SnS low temperature phase are shown for comparison. The measurement result of Example 1 is in good agreement with the SnS low-temperature phase pattern. The minute peaks around 44 ° and 46 ° are considered to be γ-Sn phases.

  The results of analyzing the raw powder and the produced high-purity tin sulfide (SnS) particles by the ICP method are shown in Table 1 (unit is ppm by mass). From the results in Table 1, it can be seen that Bi, Fe, Sb, As, and P are 100 ppm or less. Moreover, Sn / S ratio (y / z ratio) was 0.99 by fluorescent X-ray analysis.

<Preparation of copper-added tin sulfide sintered body (Sn _0.96 Cu _0.04 S)>
0.25 g of copper sulfide (Cu ₂ S) (manufactured by High Purity Chemical) is added to 12.25 g of the high purity tin sulfide (SnS) powder produced under the above conditions and mixed in a mortar, and the same operation is repeated four times. A mixed powder of 50 g was produced. The concentration of Cu in the mixed powder was 3.7 mol% (Cu concentration = 2 wt% for Cu / Sn + Cu) in terms of the ratio of metal element (Sn + Cu).

The obtained mixed powder was sintered by a hot press (HP) method. It was placed in a graphite mold having an inner diameter of 50 mmφ, placed in a hot press (manufactured by Daia Vacuum), and pressurized at a surface pressure of 75 kg weight / cm ² . BN was applied to the graphite mold with BN spray (Rubi BN, manufactured by Showa Denko) and dried. Thereafter, the surface pressure was set to 0, the inside of the furnace was evacuated to 2 × 10 ⁻³ Pa, and heated to 680 ° C. at a temperature rising rate of 10 ° C./min. At a temperature of 550 ° C. during the temperature increase, pressurization was started at a surface pressure of 75 kgf / cm ^{2. When the} temperature reached 600 ° C., N ₂ gas was allowed to flow, and then atmospheric pressure was reached in about 20 minutes. Thereafter, N ₂ gas was allowed to flow at a flow rate of 3 L / min. After reaching the holding temperature of 680 ° C., it was held for 1 hour, and at the same time as the holding was completed, the surface pressure was reduced to 0 and cooled. After cooling, the sintered body was taken out. At that time, a part of the melt extruded to the outside of the mold adhered.

  The BN powder adhering to the surface of the sintered body was scraped off with sandpaper. The weight and outer dimensions of the sintered body were measured, and the density was measured. Also, the surface electrical resistance (surface resistivity Ω / □) was measured with a four-end needle surface resistivity meter (Loresta IP MCP-T250, manufactured by Mitsubishi Chemical Corporation), and the volume resistivity (Ω · cm) was obtained by multiplying the thickness of the sample. The specific resistance was obtained by conversion. The obtained density and specific resistance are shown in Table 2. Moreover, the sintered compact was analyzed with the fluorescent X-ray apparatus and the density | concentration of Cu in a sintered compact was measured. As a result, it was 0.5 wt%. Moreover, Sn / S ratio (y / z ratio) was 0.99 by the fluorescent X ray analysis of the obtained sintered compact.

<Example 2>
A copper-added tin sulfide sintered body was produced in the same manner as in Example 1 except that the pressure of the hot press (HP) was changed to a surface pressure of 150 kg weight / cm ^2, and the density and specific resistance were measured. The results are shown in Table 2. Moreover, Sn / S ratio (y / z ratio) was 0.99 by the fluorescent X ray analysis of the obtained sintered compact.

<Example 3>
A copper-added tin sulfide sintered body was prepared in the same manner as in Example 1 except that the mixed concentration of tin sulfide (SnS) powder and copper sulfide (Cu ₂ S) was 7.3 mol%, and the density and specific resistance were adjusted. It was measured. The results are shown in Table 2. Moreover, Sn / S ratio (y / z ratio) was 0.99 by the fluorescent X ray analysis of the obtained sintered compact.

<Example 4>
A copper-added tin sulfide sintered body was prepared in the same manner as in Example 1 except that the mixed concentration of tin sulfide (SnS) powder and copper sulfide (Cu ₂ S) was 1.9 mol%. Was measured. The results are shown in Table 2. Moreover, Sn / S ratio (y / z ratio) was 0.99 by the fluorescent X ray analysis of the obtained sintered compact.

<Example 5>
A copper-added tin sulfide sintered body was produced in the same manner as in Example 1 except that the holding temperature of the hot press (HP) was 720 ° C., and the density and specific resistance were measured. The results are shown in Table 2. Moreover, Sn / S ratio (y / z ratio) was 0.99 by the fluorescent X ray analysis of the obtained sintered compact.

<Example 6>
A tin sulfide sintered body was produced in the same manner as in Example 1 except that a sintered body was produced only from a tin sulfide (SnS) powder raw material without adding copper sulfide (Cu ₂ S), and the density and specific resistance. Was measured. The results are shown in Table 2. Moreover, Sn / S ratio (y / z ratio) was 0.99 by the fluorescent X ray analysis of the obtained sintered compact.

<Example 7>
A tin sulfide sintered body was produced in the same manner as in Example 6 except that the holding temperature of the hot press (HP) was 720 ° C., and the density and specific resistance were measured. The results are shown in Table 2. Moreover, Sn / S ratio (y / z ratio) was 0.99 by the fluorescent X ray analysis of the obtained sintered compact.

<Example 8>
A tin sulfide sintered body was produced in the same manner as in Example 6 except that the holding temperature of the hot press (HP) was 720 ° C., and the pressure was 300 kgf / cm ^2, and the density and specific resistance were measured. . The results are shown in Table 2. Moreover, Sn / S ratio (y / z ratio) was 0.99 by the fluorescent X ray analysis of the obtained sintered compact.

<Example 9>
A copper-added tin sulfide sintered body was produced in the same manner as in Example 1 except that the holding temperature of the hot press (HP) was 550 ° C., and the density and specific resistance were measured. The results are shown in Table 2. Moreover, Sn / S ratio (y / z ratio) was 0.99 by the fluorescent X ray analysis of the obtained sintered compact.

<Example 10>
The concentration of Cu in the mixed powder was set to 3.7 mol% in terms of the ratio of metal element (Sn + Cu), and the mixed powder was put into a silicone rubber mold, and the pressure was 2000 kgf / cm ^{2 at} a pressure of 2000 kgf / cm ^2. A molded body was produced. The molded body was put into a hot press apparatus and sintered at a holding temperature of 680 ° C. and a holding time of 4 hours. The heating rate and atmosphere were the same as in Example 1. Density and specific resistance were measured. The results are shown in Table 2. Moreover, Sn / S ratio (y / z ratio) was 0.99 by the fluorescent X ray analysis of the obtained sintered compact.

<Example 11>
A high-purity SnS powder was produced by setting the ratio of Sn and S to 2: 5 as the raw material tin sulfide powder. The Sn / S ratio of the SnS powder by fluorescent X-ray was 0.92 in terms of molar ratio. From the XRD measurement, a small amount of Sn ₂ S ₃ phase was mixed in the SnS phase. A sintered body was produced in the same manner as in Example 1 except that this SnS powder was used, and the density and specific resistance were measured. The results are shown in Table 2. Moreover, Sn / S ratio (y / z ratio) was 0.92 by the fluorescent X ray analysis of the obtained sintered compact.

<Comparative Example 1>
Only SnS powder made by Nihon Chemical Co., Ltd. with a purity of 99.5% was used as the raw material tin sulfide powder, without adding copper sulfide, the holding temperature of the hot press (HP) was 680 ° C., and the holding time was 4 hours. Except for the above, a sintered body was produced in the same manner as in Example 1, and the density and specific resistance were measured. The results are shown in Table 2. The analysis results of SnS are shown in Table 1. The concentration of Fe was as high as 125 ppm.

<Comparative Example 2>
A sintered body was prepared in the same manner as in Example 1 except that SnS powder made by Nihon Chemical Co., Ltd. having a purity of 99.5% was used as the raw material tin sulfide powder, and the density and specific resistance were measured. The results are shown in Table 2.

<Comparative Example 3>
A sintered body was produced in the same manner as in Example 1 except that the holding temperature of the hot press (HP) was 480 ° C., and the density and specific resistance were measured. The results are shown in Table 2.

<Comparative Example 4>
A copper-added tin sulfide sintered body was produced in the same manner as in Example 1 except that the mixed concentration of tin sulfide (SnS) powder and copper sulfide (Cu ₂ S) was changed to 33.3 mol%. Most of it flowed out of the mold and solidified, and a thin plate-like sintered body remained in the mold. It was found that the sintered body could not be removed from the mold, and with this addition amount, it was difficult to produce a copper-added tin sulfide sintered body by the HP method.

<Comparative Example 5>
The same method as in Example 1 except that SnS powder made by Nihon Chemical Co., Ltd. having a purity of 99.5% was used as the raw material tin sulfide powder, the holding temperature of the hot press (HP) was 680 ° C., and the holding time was 4 hours. A sintered body was prepared and the density and specific resistance were measured. The results are shown in Table 2. The analysis results of SnS are shown in Table 1. The concentration of Fe was as high as 125 ppm.

<Comparative Example 6>
A high-purity SnS powder was prepared by using a tin sulfide powder as a raw material at a Sn: S ratio of 1: 4. The Sn / S ratio of the SnS powder by fluorescent X-ray was 0.8 in molar ratio. From the XRD measurement, the SnS phase and the SnS ₂ phase were mixed. A sintered body was produced in the same manner as in Example 1 except that this SnS powder was used, and the density and specific resistance were measured. The results are shown in Table 2. Moreover, Sn / S ratio (y / z ratio) was 0.8 by the fluorescent X ray analysis of the obtained sintered compact.

[Evaluation of performance]
For a low resistance composition system capable of DC sputtering, a discharge test was actually performed with a sputtering apparatus.

[Sputtering method]
As shown in FIG. 4, a sintered body was stuck on a Cu backing plate to prepare a target. The target was attached to a magnetron RF sputtering apparatus (SPF210H manufactured by Anelva) to form a film. After pulling to 2 Pa with a rotary pump, the vacuum was further pulled to 8 × 10 ⁻⁴ Pa with a cryopump. Thereafter, Ar gas was put in, and the sputtering pressure was 0.2 to 1.5 Pa, and the DC power source was discharged at 100 W using MDX manufactured by Advance Energy.

  The targets of Examples 1 to 11 had areas that were stably discharged when the Ar gas pressure and the distance between the target and the substrate (distance between T / S) were changed, and were actually capable of DC sputtering.

  In contrast, Comparative Examples 1 to 3 and 5 caused DC discharge when the Ar gas pressure and the distance between the target and the substrate were changed, but the discharge was partially unstable and the discharge disappeared in a short time. This is because the specific resistance within the target varies, the high resistance portion is charged, an abnormal discharge phenomenon such as spark discharge occurs, the discharge becomes unstable, and when the surface potential of the target becomes higher, the Ar ions become the target. Discharge stopped because it was not hit.

The sintered body of Comparative Example 6 was also capable of DC discharge, but abnormal discharge (partially charged at a high resistance portion and arc discharge instantaneously occurred) was observed. This high purity tin sulfide powder of Comparative Example 6 is a mixture of SnS and SnS _2, since in sputtering SnS ₂ is generated SnS and S is decomposed, often places of SnS ₂ in the target is It is thought that part of it was dug deeply, which caused abnormal discharge. On the other hand, in Examples 1 to 11, the number of occurrences of abnormal discharge decreased.

  FIG. 8 shows voltage changes during sputtering in Example 1 and Comparative Example 5. Although the voltage of Example 1 is stable, the voltage is changed in Comparative Example 5. Abnormal discharge occurred when the voltage changed. In addition, the voltage of Example 1 changed in 40 minutes of sputtering time, but this is due to the closing of the shutter above the cathode, and thus the voltage has changed due to the occurrence of abnormal discharge. Do not mean.

  FIG. 7 shows an SEM photograph of the surface of Comparative Example 5 after sputtering. Protrusions existed on the surface, and it was found that a layer containing a large amount of Cu was formed when the apex of the convex portion was analyzed by EDX. It seems that layers with different sputter speeds were deposited in the target, resulting in digging and nodules.

Claims (4)

Bi, Fe, Sb, As, P are each 100 ppm or less by mass ratio,
Specific resistance is 0.001Ω · cm~10Ω · cm, in the composition formula _{(Sn y S z) 1-} x (Cu 2 S) x, is 0 ≦ x ≦ 0.01, y / z ratio 0 A tin sulfide sintered body characterized by being in the range of 90 to 1.01.   The tin sulfide sintered body according to claim 1, containing 100 ppm or more and less than 10,000 ppm of Cu or Ag.   The tin sulfide sintered body according to claim 1 or 2, which is used as a target for DC sputtering. In the composition formula _{(Sn y S z) 1-} x (Cu 2 S) x, is 0 ≦ x ≦ 0.01, sulfide for DC sputtering target ratio y / z is 0.90 or more 1.01 or less A method for producing a tin sintered body,
A tin sulfide powder containing 0 to 0.01% by mass of Cu, Bi, Fe, Sb, As, P is 100 ppm or less by mass ratio, and an average particle size is 100 μm or less,
A method for producing a tin sulfide sintered body, wherein the tin sulfide powder is sintered by the following A) or B) to obtain a sintered body.
A) A normal pressure sintering method in which the temperature is maintained at 600 to 800 ° C. in an inert gas atmosphere under normal pressure.
B) A hot press method in which the material is heated and held in an inert gas atmosphere at a pressure of 15 kg weight / cm ² or more and 400 kg weight / cm ² or less at a temperature of 500 to 800 ° C.